The present invention relates generally to fluid seal assemblies, and more particularly, to the combination of fluid seal units with specialized protective filter units, whereby a seal assembly may be provided which will operate in an improved, trouble-free manner in use. The invention relates, in one aspect, to a specialized protective filter unit which is adapted for use with a fluid seal, as well as to the combination of a protective filter unit with an associated seal unit to form a novel seal assembly. The invention provides a seal of increased reliability, particularly in those specialized seals wherein high internal pressure and the possibility of particulate contaminants are present.
Modern fluid seals are extremely versatile in use, and are capable of sealing oil, for example, under varying conditions of pressure and temperature, without leakage, over a life span of millions of machine cycles. A typical oil seal used in a hydraulic circuit application now generally comprises a stiff exterior casing element, such as a metal stamping or the like which has an elastomeric seal lip body bonded thereto. The casing may be partially or entirely surrounded with the elastomeric material for the purpose of locating and mounting the seal within an associated machine part, i.e., in a housing counterbore.
The lip portion of the elastomeric seal body rides over a rotary or reciprocating shaft or one which undergoes both motions in use. In particular, in a number of hydraulic mechanisms, including automotive power steering units, oil or like hydraulic fluid may be maintained within a sealed cavity under extreme pressures, which may range up to 500 to 2,000 psi or more. The seal which retains oil in a cavity forming the interior of such mechanism, usually includes a primary lip, and often also includes one or more auxiliary or excluder lips formed as a part of the primary seal lip, or formed separately and used with another component which is associated with the seal unit in use.
Power steering mechanisms, particularly the rack and pinion type, include a reciprocable shaft or rack having end portions which move into and out of the sealed region, assisted by strong forces which are in turn generated in the hydraulic fluid which the seal is called upon to confine. Existing seal designs are fully capable of retaining such fluid within the sealed region, even under these high pressure conditions, for an extremely high number of cycles, as long as a proper sealing environment is maintained.
Such performance, however, depends on the presence of proper working conditions. For seals to perform in this manner, the sealed part which reciprocates relative to the seal must have a surface finish falling within closely defined limits, and the design of the mechanism must permit a generous supply of fluid to be present at the seal-shaft interface. In many cases, an otherwise satisfactory seal will leak or a sealed part may be seriously scored or otherwise damaged if contaminants present in the fluid to be sealed reach this interface. Thus, in a typical automotive power steering application, if metal chips or other remnants from the machining process find their way into the hydraulic fluid, these particles may lodge between the seal lip and the sealed part. With the passage of time and continual reciprocation of the sealed part, a score or groove may develop in the part to a degree sufficient to cause seal leakage; in some cases the damage is such that not only the seal but also the shaft or other element must also be replaced.
Needless to say, the expense of replacing sealed parts forming portions of a hydraulic mechanism can be considerable, especially where the high cost of skilled labor and the inconvenience of gaining access to the sealed part are considered. Still further, the end user of a product of this sort may perceive an oil leak and/or the requirement for replacing part of an important mechanism to be a reflection of low vehicle quality, with extremely adverse overall consequences for the manufacturers and marketers of the vehicles in question. The same considerations also apply in respect to those suppliers who furnish components or subassemblies to manufacturers and/or assemblers of vehicles.
Consequently, there has been a need for an improved seal system which will, where possible, ensure that failure to provide exceptionally clean individual machine elements will not result in a subsequent seal failure with a concomitant large expense, loss of reputation for quality and in some cases, total failure of expensive, sealed machine parts.
In the manufacture of hydraulic assemblies, including power steering units, it is well known that complex machining operations, including boring, honing, counterboring, drilling, tapping, end facing and other finishing steps, are required. These operations are usually performed in sequence on highly complex, automated machinery. When the machining and finishing cycles are completed, the part is intended to be cleaned so that no chips or other residue from the machining operation remain in the finished part.
However, as in other highly automated and engineered products, there is always a potential for an isolated failure, and as a result there has been a need for a product such as that provided by the present invention, which will further forestall the possibility of such failure, and preferably do so with high reliability at low cost.
According to the invention a seal system with an improved form of protective filter unit and wiper lip is provided, in which a protective filter unit is used in tandem with an existing high pressure seal, with the filter being positioned so that it will entrap whatever filings or scrap may be present in the fluid and either retain them on the face of the seal or confine them to an area wherein they are not wedged by a strong hydraulic action between the seal lip and the reciprocable part.
In this connection, it will be appreciated that modern hydraulic seals are designed in such a way that, as the pressure in the sealed cavity rises, this pressure is exerted around the outer periphery of the elastomeric seal lip body, and this in turn applies an increased radial compressive sealing load through the elastomer to the surface of the sealed part. In other words, as hydraulic pressure tending to cause leakage rises, the sealing force generated at the sealing lip-machine element interface rises correspondingly to offset this tendency or potential to leak. Thus, the seal is basically not affected by pressure.
According to the present invention, improved filter elements are provided which are capable of separate manufacture, but insertion in use in tandem with existing seals to form a novel seal system and sealed mechanism.
In view of the failure of prior art seals to provide wholly satisfactory contaminant reduction and/or control action presently required of hydraulic mechanisms, including power steering units, it is an object of the present invention to provide an improved protective filter assembly for use with a seal to form a sealed hydraulic mechanism.
Another object of the invention is to provide a combination novel protective filter unit and fluid seal assembly capable of preassembly and strong retention as a unit before during and after being inserted in a portion of the sealed mechanism, so that it is unaffected by variations of pressure and temperature.
A further object is to provide a seal assembly which includes an operationally integral filter unit adapted to protect the so-called oil side of the seal from contamination by fluid-borne shavings, or other abrasive residues.
Another object of the invention is to provide a protective filter unit for an oil seal, which filter unit is made from readily available materials by existing technology and which may therefore be mass produced at low cost.
A still further object of the invention is to provide a protective filter unit for a seal assembly which includes a ring or casing adapted for registration and interfitting with an associated seal unit and which includes, in addition to the ring or casing, a radially inwardly extending protective filter screen affixed to the ring or casing and a wiper lip on the inside diameter of the seal.
Yet another object of the invention is to provide a protective filter unit for a fluid seal, which filter unit includes an outer support ring able to be affixed to the casing of an associated seal unit, and having an excluder lip and a second filter on its inner diameter, in flexible contact with a shaft, with a filter means in between the inside and outside diameters to prevent the associated seal from contamination by particles in the sealed fluid.
It is also an object of the invention to provide a seal assembly which includes a protective filter unit, and a high pressure seal assembly which includes a casing and an elastomeric seal body, with the casing and a portion of the seal body cooperating to form a permanent mounting surface for the filter unit, and wherein the filter unit includes an exterior casing unit with portions of the filter unit and the seal casing being lockingly engageable with each other whereby the filter and the oil side wiper lip may be permanently located with respect to the remainder of the seal.
A still further object of the invention is to provide a multipart seal assembly which includes one form or another of filter element, a seal element permanently affixable to the filter unit, and an auxiliary element which includes an anti-extrusion or backup support unit for the elastomeric primary seal lip body of the seal element, with an auxiliary or excluder lip having portions engaging the interior surface of the sealed region.
A still further object of the invention is to provide a sealed mechanism which includes a housing, a machine element having a part reciprocable into and out of the housing and a composite seal assembly for the housing and the reciprocable part, with the seal assembly including a primary seal unit having a casing and an elastomeric seal lip portion, a protective filter unit disposed axially inwardly of the primary seal unit and including a filter element, with the seal assembly further including at least one auxiliary or excluder lips, with a backup or pressure absorbing element for portions of the body of the primary seal lip.